Light emitting diode (LED) is widely used for displaying information and message. LED is a solid state device that converts electric energy to light and requires reduced operational voltage and current. LED provides a higher level of brightness and greater optical efficiency as compared to other types of display panels.
The LED display panel includes an LED array and a plurality of driver chips. The total number of the M×N LED driver chips can vary depending on the size and resolution of the LED display panel.
For example, a high definition LED display panel may require 1,280×720 pixels or more. If each driver chip controls 64×16 LED pixels, then it will need a total of 900 driver chips. If 900 chips start to operate at the same time in response to a single serial clock signal, it will cause problematic electromagnetic radiation, such as Electromagnetic Interefernce (EMI).
To attenuate EMI radiation, the spread spectrum modulation depth controller can be used so that a modulation is performed with respect to the input frequency of a reference clock signal in an LED driver chip to spread the spectrum of an output clock signal, thereby reducing the peak value of EMI. Spread spectrum modulation depth controller provides modulated frequency so that the energy is spread out over a wider bandwidth. The attenuation achieved by the spread spectrum modulation depth controller is relative to the length of the horizontalness of the energy spectrum. The more evenly energy is spread over the bandwidth, the more attenuation is achieved.
However, when a plurality of spread spectrum modulation depth controllers are used, it is considerably more difficult to synchronize them, causing increased clock jitters and thus a new solution is required to change the spread spectrum modulation depth. Furthermore, a spread spectrum modulation depth controller usually comes with less than +/−1% spread spectrum modulation depth limit. Accordingly, apparatus and method that overcome the above described shortcomings are needed.